Tissue products, such as facial tissues, paper towels, bath tissues, and the like, are designed to provide good bulk, a soft feel, and good strength and durability. Unfortunately, however, when steps are taken to increase one property, other characteristics are often adversely affected. For example, softness must generally be balanced against strength and durability. Durability in tissue products can be defined in terms of tensile strength, tensile energy absorption (TEA), burst strength and tear strength. Typically tear, burst and TEA will show a positive correlation with tensile strength while tensile strength, and thus durability, and softness are inversely related. Thus the paper maker is continuously challenged with the need to balance the need for softness with a need for strength and durability.
To achieve an optimal balance of softness and strength, the tissue maker typically relies upon blending wood pulp fibers having different physical properties such as fiber length and fiber coarseness. For example, easily collapsible, low coarseness long fibers, such as Northern softwood kraft (NSWK) fibers are commonly combined with short, low coarseness hardwood kraft fibers such as Eucalyptus hardwood kraft (EHWK) fibers. The long, low coarseness fibers provide strength and durability without overly stiffening the tissue web, while the short low coarseness fibers provide a soft hand feel and minimal strength development. The benefits of the various fiber types may be further enhanced by forming a layered tissue web in which the different fibers are selectively deposited in certain layers to provide maximal benefit.
While NSWK provides many benefits to the tissue maker, the supply of NSWK is under significant pressure both economically and environmentally and alternatives are limited. For example, southern softwood kraft (SSWK) may only be used in limited amounts in the manufacture of tissue products because its high coarseness results in stiffer, harsher feeling products than NSWK. Thus, there remains a need for an alternative to NSWK for the manufacture of tissue products, which must be both soft and strong.